The case is being heard in the High Court at Auckland, where yesterday art consultant and gallery owner Patricia Clark, who has represented some of New Zealand's leading artists, including Bambury and Billy Apple, gave evidence.
Ms Clark, known as Trish, described herself as a friend of Bambury, and helped him when he claimed a number of his works were unaccounted for after his relationship with Mr Jensen broke down.
Bambury contacted her in early 2010 after speaking to a woman who had bought one of his artworks without his knowledge, she said.
"He believed he had not been paid by Andrew Jensen," she said, later adding: "He was worried he had not been paid for other works."
Bambury was "very troubled" by this, she said, and after discussing it with him she advised him to leave the gallery. "He looked shocked when I suggested this course of action. I told him he was in a vulnerable position as Andrew held so much of his work."
Ms Clark said she believed Mr Jensen would "react badly" if Bambury tried to confront him, so she advised him to "dissemble a little" from the gallery, and ask for his work back to do a stock-take.
Shortly afterwards, she said: "Stephen called me and told me Andrew had fired him."
She described Mr Jensen as "a difficult person to work with" but at that stage she "did not consider him to be dishonest with his artists".
However, when Bambury started his stock-take he realised "a huge group of works" were missing which he had no record of selling.
She then set about helping him identify what happened to the artworks, saying: "I presumed Andrew would have information to relieve all queries, and that if there were works that Stephen had not been paid for, Andrew would pay him."
Letters were exchanged between lawyers, but information was not forthcoming, she said. The decision was made to take the matter to court.
Gallery owner Michael Lett, who represents Michael Parekowhai and Shane Cotton, among others, at his gallery on Karangahape Rd, gave evidence as an expert witness about the relationship between a gallerist/agent and an artist, and the normal level of commission an agent would charge.
Mr Jensen is also accused of several other claims, including buying a Bambury artwork for the purposes of on-selling for a profit during the time he was acting as his agent, breaching the terms of their contract.
He denies the claims. The case continues.